1. Field of the Invention
The present invention generally relates to a hydraulic blow system employing a one-step container molding process wherein a preform is initially formed in a machine and a container is subsequently molded in the same machine or at a different machine while utilizing the latent heat, from the initial forming of the preform, in the subsequent forming of the container. More specifically, the invention relates to sealing of the forming head with the preform during the hydraulic blow molding process used to form the container.
2. Description of Related Art
Plastic containers for liquid products are manufactured by various different methods. In some methods, a plastic preform is injection molded in a preform molding machine and subsequently cooled to ambient temperatures. In a second machine, which may be in a remote location, the preform is re-heated to a suitable temperature for molding, placed within a mold and then expanded, axially and radially, to form a container. Such a process is known as a two-step molding process, and a corresponding system is known as a two-step system.
In another process, the injection molding of the preform and the subsequent forming of the container all occur in the same machine or in different machines, but without allowing the preform to significantly cool and require reheating. Such processes and systems are correspondingly known as one-step processes and systems.
In either of the above processes, air may be used as the blow medium to axially and radially expand the preform and form the container. When forming the container with air, the forming head is provided with a sealing collar that extends interiorly along the finish of the preform. The sealing collar engages the inner diameter of the finish and establishes establish an interference fit or seal between the forming head and the preform. Additionally, when the container is formed by injecting pressurized air, the sealing mechanism between the air injection head and the preform only needs preventing from excessive air leaks. The need is to reduce the quantity of highly pressurized air requested for forming the container and to reduce noise.
Instead of air as the blow medium, newer processes use the liquid end product as the blow medium. This process is herein referred to as hydraulic blow molding. With hydraulic blow molding, if the seal between the forming head and the preform is insufficient to retain the liquid blow medium, the leaked liquid blow medium may contaminate various surfaces of the molding machines components, which may in turn inhibit or disrupt the further manufacture of preforms and containers. As a result, the contaminated machine may experience downtime and require extensive cleaning, both of which are undesirable from a production standpoint.
U.S. patent publication no. US2013/0164404 describes a sealing system for forming a container from a preform with a forming fluid which may be liquid. The sealing system is provided with two sealing engagements. An elastomeric seal extends between the blow nozzle and the finish of the preform. A valve system can be used to remove residual liquid between the elastomeric seal and the second seal engagement.
In view of the above, it is apparent that there is a need for a robust sealing strategy in one-step hydraulic blow molding machines or systems.